JP5217645B2 - Electrolytes and electrochemical devices - Google Patents

Description

  The present invention relates to an electrolyte and an electrochemical device including the electrolyte as an electrolyte layer.

  As an electrolyte material that does not easily cause liquid leakage, an electrochemical device using a polymer as an electrolyte has attracted attention.

For example, the polymer used in the electrolyte of the lithium polymer battery, polyethylene oxide _{(PEO, - [CH 2 CH} 2 O] m -) can be mentioned. In addition, since such a polymer is not a flame-retardant thing, development of the lithium polymer battery provided with the flame retardance is calculated | required.

As a highly flame retardant material, for example, a fluorine-based material can be considered. As the fluorine-based material, for example, Patent Document 1 describes a separator containing a fluorine-containing imide polymer.
Japanese Patent Laid-Open No. 10-228893

  By the way, the electrolyte used for the conventional electrochemical device did not fully satisfy a high cation transport number.

  Therefore, an object of the present invention is to provide an electrolyte having a high cation transport number and an electrochemical device comprising the electrolyte as an electrolyte layer.

  In order to achieve the above object, the present invention provides an electrolyte comprising a lithium polymer salt having a structure represented by the following general formula (1).

Here, in Formula (1), A ¹ and A ² each independently represent a carbonyl group or a sulfonyl group, and R ¹ and R ² represent a divalent organic group. N represents a positive integer of 2 or more. A plurality of A ¹ , A ² , R ¹ and R ² in the same molecule may be the same or different.

  By having such a configuration, the electrolyte of the present invention has a high cation transport number. The high cation transport number in the electrolyte of the present invention is achieved mainly for the following two reasons.

As the first reason, in the above-described polymer lithium salt, a group adjacent to N, that is, A ¹ and A ² are a carbonyl group (—CO—) or a sulfonyl group (—SO ₂ —). . Since these groups have high electron-withdrawing properties, the degree of dissociation of lithium ions can be improved by using such a structure.

The second reason is that the lithium salt used in the electrolyte of the present invention is a polymer lithium salt, that is, the molecular weight of the anion portion is large. Usually, a monomer salt is used as a lithium salt of a lithium polymer battery. However, such a monomer salt can move the anion dissociated in the electrolyte without receiving an interaction with the polymer chain, so that the conductivity (σ ⁻ ) of the anion is increased. Therefore, the lithium ion transport number (t ⁺ = σ ⁺ / (σ ⁺ + σ ⁻ ) = σ ⁺ / indicating the proportion of the lithium ion conductivity (σ ⁺ ) in the total ion conductivity (σ = σ ⁺ + σ ⁻ ). σ) is quite low and may be 0.1 or less. On the other hand, since the polymer lithium salt used in the electrolyte of the present invention has a large molecular weight of the anion portion, the anion conductivity (σ ⁻ ) can be very low, and as a result, the cation transport number is improved. .

R ¹ is preferably an alkylene group, an arylene group, an alkenylene group or an alkylene ether group, and R ² is preferably an alkylene group, an arylene group, an alkenylene group or an alkylene ether group. When R ¹ and R ² have such a structure, the cation transport number is further improved.

R ¹ and R ² are preferably a divalent organic group substituted with a fluoro group. That is, the divalent organic group represented by R ¹ and R ² is preferably partially fluorinated or fully fluorinated. When R ¹ and R ² contain a fluorine element, flame retardancy can be imparted.

  The lithium polymer salt can be mixed with an aprotic solvent to form an electrolyte. That is, the electrolyte of the present invention can further contain an aprotic solvent. By dissolving the lithium polymer salt in an aprotic solvent, fluidity can be imparted to the electrolyte, which makes it easy to use in various electrochemical devices.

  The electrolyte of the present invention preferably further contains a polymer material different from the lithium polymer salt. When the electrolyte further includes such a material, the electrolyte has excellent mechanical strength.

The electrolyte of the present invention preferably further contains a fluoropolymer having a repeating unit represented by the following general formula (2).

  The electrolyte of the present invention is excellent in flame retardancy, flexibility and processability by further including a fluoropolymer having such a structure.

  The present invention further provides an electrochemical device comprising the above-described electrolyte as an electrolyte layer. Since such an electrochemical device includes the above-described electrolyte as an electrolyte layer, it has a high cation transport number. The electrochemical device may be a lithium polymer battery. Such a lithium polymer battery has a high cation transport number.

  ADVANTAGE OF THE INVENTION According to this invention, an electrochemical device provided with an electrolyte with a high cation transport number and this as an electrolyte layer can be provided. Moreover, the electrochemical device of the present invention can be used as a lithium polymer battery.

  Hereinafter, preferred embodiments of a lithium polymer battery as an electrochemical device will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and redundant description is omitted. Further, the positional relationship such as up, down, left and right is based on the positional relationship shown in the drawings unless otherwise specified. Further, the dimensional ratios in the drawings are not limited to the illustrated ratios.

  FIG. 1 is a schematic cross-sectional view showing a basic configuration of a preferred embodiment of a lithium polymer battery of the present invention. A lithium polymer battery 1 shown in FIG. 1 mainly includes an anode 2 and a cathode 3 and an electrolyte layer 4 disposed between the anode 2 and the cathode 3. Here, the anode 2 and the cathode 3 are determined based on the polarity at the time of discharging of the lithium polymer battery 1 for convenience of explanation. Therefore, during charging, the anode 2 becomes a “cathode” and the cathode 3 becomes an “anode”.

  In the lithium polymer battery 1, a film-like (plate-like, layered) current collector (anode current collector) 5 is provided on the surface of the anode 2 opposite to the electrolyte layer 4, and the cathode 3. A film-like (plate-like, layer-like) current collector (cathode current collector) 6 is provided on the surface opposite to the electrolyte layer 4. Moreover, the shape of the anode 2 and the cathode 3 is not specifically limited, For example, thin film shape (layer shape) may be sufficient as shown in figure.

  The electrodes, that is, the anode 2 and the cathode 3 may be appropriately selected from those known as electrodes of lithium ion secondary batteries, and a composition obtained by mixing an electrode active material and an electrolyte is used. Is also possible.

  The anode 2 is preferably a negative electrode active material such as a carbon material, lithium metal, lithium alloy, or oxide material. The carbon material may be appropriately selected from, for example, mesocarbon microbeads (MCMB), natural or artificial graphite, resin-fired carbon material, carbon black, carbon fiber, and the like. These are used as powders.

  Although the thickness in particular of the anode 2 is not restrict | limited, For example, it is 0.1-300 micrometers, and it is more preferable that it is 1-150 micrometers.

For the cathode 3, it is preferable to use a positive electrode active material such as an oxide or carbon capable of intercalating and deintercalating lithium ions. The oxide capable of intercalating and deintercalating lithium ions is preferably a composite oxide containing lithium, and examples thereof include LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , and LiV ₂ O ₄ . The average particle size of the oxide powder is preferably about 1 to 40 μm.

  Although the thickness in particular of the cathode 3 is not restrict | limited, For example, it is 0.1-300 micrometers, and it is more preferable that it is 1-150 micrometers.

  A conductive additive is added to the electrode as necessary. Preferred examples of the conductive aid include metals such as graphite, carbon black, carbon fiber, nickel, aluminum, copper, and silver, and graphite and carbon black are particularly preferable.

  Moreover, a gel electrolyte can be added to the electrode as a binder. The electrode composition in this case is preferably in the range of active material: conducting aid: gel electrolyte = 10-50: 0-20: 30-90 by weight for the cathode (positive electrode) and weight for the anode (negative electrode). The ratio of active material: conductive aid: gel electrolyte = 10-50: 0-20: 30-90 is preferable. An electrode using a substance other than the gel electrolyte as the binder is also preferably used. In this case, a fluororesin, fluororubber, or the like can be used as the binder, and the amount of the binder is about 3 to 30% by weight with respect to the weight of the entire electrode. As the binder, a lithium polymer salt electrolyte having a structure represented by the general formula (1) can also be used.

  The electrolyte layer 4 includes a lithium polymer salt having a structure represented by the following general formula (1), and plays a role as a polymer electrolyte and a role as a lithium salt.

Here, in Formula (1), A ¹ and A ² each independently represent a carbonyl group or a sulfonyl group, and R ¹ and R ² represent a divalent organic group. The carbonyl group is a divalent group represented by [—CO—], and the sulfonyl group is a divalent group represented by [—SO ₂ —]. N represents a positive integer of 2 or more. A plurality of A ¹ , A ² , R ¹ and R ² in the same molecule may be the same or different.

Either A ¹ or A ² is preferably a sulfonyl group, more preferably both A ¹ and A ² are sulfonyl groups. Since sulfonyl groups have higher electron-withdrawing properties than carbonyl groups, the more sulfonyl groups, the higher the degree of dissociation of lithium ions. R ¹ is preferably an alkylene group, an arylene group, an alkenylene group or an alkylene ether group, and R ² is preferably an alkylene group, an arylene group, an alkenylene group or an alkylene ether group. When R ¹ and R ² have such a structure, the cation transport number can be further improved.

R ¹ and R ² are preferably a divalent organic group substituted with a fluoro group. When R ¹ and R ² contain a fluorine element, flame retardancy can be imparted and safety can be improved. Furthermore, it is strong against oxidation and reduction. Moreover, compatibility with the fluoropolymer represented by the following formula (2) can be improved by making the lithium polymer salt into such a structure.

Examples of the structure represented by [—R ² —R ¹ —] include structures represented by the following formulas (i) to (xxix).

In the formulas (i) to (xxix), m and r each represent a positive integer of 1 or more. From the viewpoint of cation transport number, m and r are preferably 15 or less. In the formula ^(iv), R 3 ~R ⁶ _{may, H, F, C 1 ~C} 5 - alkyl - alkyl or partially fluorinated or perfluorinated been _C 1 -C _5.

  The lithium polymer salt having a repeating unit represented by the general formula (1) includes, for example, hexamethyldisilazane lithium represented by the following formula (a) and a compound represented by the following general formula (b): Can be synthesized. The compound represented by the following general formula (b) may be used individually by 1 type, and 2 or more types may be mixed and used for it.

Hexamethyldisilazane lithium:

Formula (b), A ² , R ² , R ¹ and A ¹ are as defined above, and X represents a halogen element.

The electrolyte of the present invention may further contain a monomer lithium salt. That is, as the lithium salt, the above polymer lithium salt and monomer lithium salt may be used in combination. Examples of the monomer lithium salt include lithium salts such as LiBF ₄ , LiPF ₆ , LiAsF ₆ , LiSO ₃ CF ₃ , LiClO ₄ , and LiN (SO ₂ CF ₃ ) ₂ .

  The lithium polymer salt and an aprotic solvent can be mixed to form an electrolyte. That is, the electrolyte of the present invention can further contain an aprotic solvent. By dissolving the lithium polymer salt in an aprotic solvent, fluidity can be imparted to the electrolyte, which makes it easy to use in various electrochemical devices.

  The aprotic solvent is not particularly limited as long as it has good compatibility with the lithium polymer salt, but a polar organic solvent that does not decompose even at a high operating voltage is preferable when used for an electrolyte such as a lithium battery. Used. As such a polar organic solvent, for example, carbonates such as ethylene carbonate (abbreviation EC) and propylene carbonate (abbreviation PC), cyclic ethers such as tetrahydrofuran (abbreviation THF), sulfolane, lactone and the like are preferably used. Butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyldioxolane, γ-butyrolactone, 3-methylsulfolane, dimethoxyethane, diethoxyethane, ethoxymethoxyethane , Ethyl diglyme, and imidazolium salt. The aprotic solvent is not limited to this, and may be appropriately selected depending on the device to be applied.

  The concentration of the lithium polymer salt in the electrolyte is preferably 0.3 to 5 mol / L. Usually, the highest ion conductivity is exhibited when this concentration is about 1 mol / L. The lithium polymer salt / aprotic solvent in the electrolyte is preferably 3/2 to 1/9 by weight. By setting the weight ratio of the lithium polymer salt to the aprotic solvent within this range, the mechanical strength and ionic conductivity of the electrolyte can be improved.

  The electrolyte of the present invention preferably further contains a polymer material different from the lithium polymer salt. When the electrolyte further includes such a material, the electrolyte has excellent mechanical strength.

  The polymer material is not particularly limited as long as it can hold a lithium polymer salt. For example, polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chloride. Trifluoroethylene (CTFE) copolymer [P (VDF-CTFE)], vinylidene fluoride-hexafluoropropylene fluororubber, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene fluororubber [P (VDF-TFE-HFP )], Fluoropolymers such as vinylidene fluoride-tetrafluoroethylene-perfluoroalkyl vinyl ether fluororubber. Among these, polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene (HFP), and a copolymer of vinylidene fluoride and ethylene trifluoride [P (VDF-CTFE)] are preferable, and polyvinylidene fluoride. Of these resins, that is, vinylidene fluoride in the vinylidene fluoride polymer is preferably 50% by weight or more, particularly 70% by weight or more.

  The electrolyte layer 4 preferably contains a fluoropolymer composed of repeating units represented by the following general formula (2) separately from the lithium polymer salt.

  When the electrolyte layer 4 further includes a fluoropolymer having such a structure, the electrolyte layer 4 has excellent flame retardancy, flexibility, and processability. Moreover, it becomes a highly safe thing by being excellent in a flame retardance.

  In addition, as a fluoropolymer comprised from the repeating unit represented by the said General formula (2), the compound represented by a following formula (2-1) is mentioned, for example.

CF ₃ O (CF ₂ CF ₂ O) _q CF ₃ (2-1)

  Here, in formula (2-1), q represents an integer of 1 or more. From the viewpoint of cation transport number and conductivity, q is preferably 7 or more and 15 or less.

Although this type of compound is actually thermally and chemically stable, it has been difficult to use in the past because of its low solubility in conventional lithium salts such as LiPF ₆ and LiTFSI. However, if the lithium polymer salt having the structure represented by the general formula (1) is used, the dissolution ability is improved, so that the use becomes easy.

  Although the thickness in particular of the electrolyte layer 4 is not restrict | limited, For example, it is 0.1-100 micrometers, and it is more preferable that it is 0.1-15 micrometers.

  The anode current collector 5 and the cathode current collector 6 may be selected from materials generally used as current collectors according to the shape of the device using the battery, the method of arranging the current collector in the case, and the like. Good.

  The constituent material of the anode current collector 5 is not particularly limited as long as it has electron conductivity. For example, nickel, copper, or the like is used, and nickel is preferably used. Further, the constituent material of the cathode current collector 6 is not particularly limited as long as it has electron conductivity, but for example, nickel, aluminum, tantalum, iron, titanium, etc. are used, preferably nickel, aluminum, tantalum. Are used, preferably aluminum. In addition, metal foil, a metal mesh, etc. are normally used for these electrical power collectors. The metal mesh has a smaller contact resistance with the electrode than the metal foil, but a sufficiently small contact resistance can be obtained even with the metal foil.

  The lithium polymer battery of the present invention can be produced, for example, by the following steps. A coating liquid in which an anode active material and / or a cathode active material is dispersed in a binder solution or the like is applied onto the anode current collector 5 and the cathode current collector 6, respectively, and dried, whereby the anode current collector 5 and the cathode current collector are collected. An anode 2 and a cathode 3 are formed on the electric body 6. Thereafter, if necessary, the anode 2 and the cathode 3 formed by a flat plate press, a calender roll or the like are subjected to a rolling process.

  Note that the means for applying the coating liquid onto the anode current collector 5 and the cathode current collector 6 is not particularly limited, and may be appropriately determined according to the material and shape of the current collector. In general, a metal mask printing method, electrostatic coating method, dip coating method, spray coating method, roll coating method, doctor blade method, gravure coating method, screen printing method and the like are used.

  Here, the above-described binder solution may be used as necessary. Moreover, you may contain a conductive support agent in the above-mentioned coating liquid as needed. Furthermore, it is preferable that both the anode active material and the cathode active material are dispersed in the coating solution.

  After the anode 2 and the cathode 3 are formed on the anode current collector 5 and the cathode current collector 6, the cathode current collector 6, the cathode 3, the electrolyte layer 4, the anode 2, and the anode current collector 5 are arranged in this order. Laminate and crimp.

  The preferred embodiment of the present invention has been described above, but the present invention is not limited to the above embodiment.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example.

[Example 1]
Further, 5.77 g of a 29 wt% tetrahydrofuran solution of hexamethyldisilazane lithium was further diluted with tetrahydrofuran (THF) to prepare 16.75 g (0.01 mol) of a 10 wt% solution of hexamethyldisilazane lithium.

  Next, 4.425 g of perfluoro-3,6,9-trioxaundecane dioil difluoride was diluted with THF, and 44.25 g of a 10 wt% solution of perfluoro-3,6,9-trioxaundecane dioil difluoride was diluted. (0.01 mol) was prepared.

Perfluoro-3,6,9-trioxaundecandioyl difluoride:

  While dropwise cooling 16.75 g (0.01 mol) of a 10 wt% solution of hexamethyldisilazane lithium with ice, 44.25 g of a 10 wt% solution of perfluoro-3,6,9-trioxaundecandioyl difluoride was added dropwise to room temperature. The temperature was raised to 12 hours and allowed to react.

  Thereafter, the precipitated polymer was separated by filtration, washed three times with diethyl ether, and vacuum dried at 100 ° C. to obtain 4.8 g of a yellowish white polymer. This polymer was dissolved in 50 ml of methanol, and then filtered to remove insoluble matters. The filtrate was dropped into 2 liters of ether, re-precipitated, and 4.5 g of lithium polymer salt was obtained by filtration and drying. . The repeating unit possessed by the obtained lithium polymer salt is represented by the following formula (1-1).

[Example 2]
Further, 5.77 g of a 29 wt% tetrahydrofuran solution of hexamethyldisilazane lithium was further diluted with tetrahydrofuran (THF) to prepare 16.75 g (0.01 mol) of a 10 wt% solution of hexamethyldisilazane lithium.

  Next, 3.825 g of bis [(fluorosulfonyl) tetrafluoroethyl] ether was diluted with THF to prepare 38.25 g (0.01 mol) of a 10 wt% solution of bis [(fluorosulfonyl) tetrafluoroethyl] ether.

Bis [(Fluorosulphonyl) tetrafluoroethyl] ether:

  While ice-cooling 16.75 g (0.01 mol) of a 10 wt% solution of hexamethyldisilazane lithium, 38.25 g of a 10 wt% solution of bis [(fluorosulfonyl) tetrafluoroethyl] ether was added dropwise, and the temperature was raised to room temperature. For 12 hours.

  Thereafter, the precipitated polymer was separated by filtration, washed three times with diethyl ether, and vacuum dried at 100 ° C. to obtain 4.2 g of a yellowish white polymer. This polymer was dissolved in 50 ml of methanol and then filtered to remove insoluble matter. The filtrate was dropped into 2 liters of ether, reprecipitated, and 3.9 g of lithium polymer salt was obtained by filtration and drying. . The repeating unit which the obtained lithium polymer salt has is shown in the following formula (1-2).

[Example 3]
Further, 5.77 g of a 29 wt% tetrahydrofuran solution of hexamethyldisilazane lithium was further diluted with tetrahydrofuran (THF) to prepare 16.75 g (0.01 mol) of a 10 wt% solution of hexamethyldisilazane lithium.

  Next, 1.913 g of bis [(fluorosulfonyl) tetrafluoroethyl] ether was diluted with THF to prepare 19.13 g (0.005 mol) of a 10 wt% solution of bis [(fluorosulfonyl) tetrafluoroethyl] ether.

  Further, 2.212 g of perfluoro-3,6,9-trioxaundecane dioil difluoride was diluted with THF, and 22.12 g of a 10 wt% solution of perfluoro-3,6,9-trioxaundecane dioil difluoride ( 0.005 mol).

  First, 22.25 g of perfluoro-3,6,9-trioxaundecane dioil difluoride 10 wt% solution was added dropwise while cooling 16.75 g (0.01 mol) of a 10 wt% solution of hexamethyldisilazane lithium. Further, 19.13 g of a 10 wt% solution of bis [(fluorosulfonyl) tetrafluoroethyl] ether was added dropwise to this solution, and then the mixture was heated to room temperature and reacted for 12 hours.

  Thereafter, the precipitated polymer was separated by filtration, washed three times with diethyl ether, and vacuum dried at 100 ° C. to obtain 4.5 g of a yellowish white polymer. This polymer was dissolved in 50 ml of methanol and then filtered to remove insoluble matters. The filtrate was dropped into 2 liters of ether, re-precipitated, and 4.1 g of lithium polymer salt was obtained by filtration and drying. . The obtained lithium polymer salt has repeating units represented by the following formulas (1-3) and (1-4) in addition to the repeating units represented by the above formulas (1-1) and (1-2). .

[Example 4]
Further, 5.77 g of a 29 wt% tetrahydrofuran solution of hexamethyldisilazane lithium was further diluted with tetrahydrofuran (THF) to prepare 16.75 g (0.01 mol) of a 10 wt% solution of hexamethyldisilazane lithium.

  Next, 3.271 g of perfluoro-3,6-dioxaoctane dioil difluoride was diluted with THF, and 32.71 g (0.01 mol) of a 10 wt% solution of perfluoro-3,6-dioxaoctane dioil difluoride was diluted. ) Prepared.

Perfluoro-3,6-dioxaoctanedioyl difluoride:

  While cooling 16.75 g (0.01 mol) of a hexamethyldisilazane lithium 10 wt% solution with ice, 32.71 g of a perfluoro-3,6-dioxaoctanedioyl difluoride 10 wt% solution was added dropwise, and the mixture was allowed to rise to room temperature. The reaction was allowed to warm for 12 hours.

  Thereafter, the precipitated polymer was separated by filtration, washed three times with diethyl ether, and vacuum-dried at 100 ° C. to obtain 3.6 g of a yellowish white polymer. This polymer was dissolved in 50 ml of methanol and then filtered to remove insoluble matters. The filtrate was dropped into 2 liters of ether, re-precipitated, and 3.3 g of lithium polymer salt was obtained by filtration and drying. . The repeating unit possessed by the obtained lithium polymer salt is represented by the following formula (1-5).

[Comparative Example 1]
LiPF ₆ was prepared as a lithium salt instead of the lithium polymer salt.

[Comparative Example 2]
LiN (SO ₂ CF ₃ ) ₂ was prepared as a lithium salt instead of the lithium polymer salt.

(Evaluation)
Various evaluation was performed using the lithium polymer salt prepared in Examples 1 to 4 and the lithium salt prepared in Comparative Examples 1 and 2.

[Solubility]
A lithium polymer salt or a lithium salt was dissolved in an equal volume ratio mixed solvent of ethylene carbonate (abbreviation EC) and dimethyl carbonate (abbreviation DEC) to prepare an electrolyte raw material having a lithium ion concentration of 1 mol / L. Here, the solubility was evaluated as “good” for those easily dissolved at room temperature and “bad” for those that did not dissolve. The evaluation results are shown in Table 1.

Next, a lithium polymer salt or a lithium salt is dissolved in a fluoropolymer represented by [CF ₃ O (CF ₂ CF ₂ O) ₄ CF ₃ ], and an electrolyte raw material having a lithium ion concentration of 1 mol / L is obtained. Got ready. A homogenizer was used for the dissolution. Here, the solubility was evaluated as “good” for those easily dissolved at room temperature and “bad” for those that did not dissolve. The evaluation results are shown in Table 1.

[conductivity]
The electrolyte raw material prepared as described above is sandwiched between stainless steel plates having a thickness of 0.145 cm and an area of 0.7854 cm ² , and the applied sine wave AC voltage is expressed by a symbolic method (complex display). The conductivity was determined from the Cole-Cole plot. The results are shown in Table 1.

[Cation transport number]
In the same manner as described above, an electrolyte raw material obtained by dissolving lithium polymer salt or lithium salt in an equal volume ratio mixed solvent of ethylene carbonate (abbreviation EC) and dimethyl carbonate (abbreviation DEC), lithium polymer salt or lithium salt [ An electrolyte raw material dissolved in a fluoropolymer represented by CF ₃ O (CF ₂ CF ₂ O) ₄ CF ₃ ] was prepared. However, with respect to the lithium ion concentration, 0.1 mol · dm ⁻³ (hereinafter referred to as “C1”), C1 / 2, C1 / 4, C1 / 8, C1 / 16 (hereinafter referred to as these concentrations). Was prepared as “C2”).

  The prepared electrolyte raw material with concentration C1 is charged into one chamber of an H-type electrolytic cell (with a glass filter at the liquid junction), and the electrolyte raw material with concentration C2 is charged into the other chamber. The electromotive force generated between the electrodes made of a provided pair of lithium metal wires was measured.

  Here, the relationship between the electromotive force and the lithium ion concentration is expressed by the Nernst equation of the following equation (3).

Here, in formula (3), E is an electromotive force, t ⁺ is a cation transport number, R is a gas constant, T is an absolute temperature (K), and F is a Faraday constant.

That is, C1 and T are fixed, C2 is changed to C1 / 2, C1 / 4, C1 / 8, and C1 / 16, E is measured, and E with respect to the natural logarithm of the concentration ratio (ln (C2 / C1)) is obtained. If plotted, the cation transport number (t ⁺ ) can be determined from the slope.

  Table 1 shows the measurement results of the cation transport number. Such a method for measuring the cation transport number (electromotive force method) is a general method, and is also described in, for example, pages 71 and 72 of the 35th Battery Discussion Meeting.

[Electrochemical stability]
Each electrolyte was prepared in the same manner as described for solubility. A three-electrode electrochemical cell was constructed using a glassy carbon electrode as the working electrode, lithium metal as the counter electrode, and lithium metal as the reference electrode. The thus produced cell was subjected to linear sweep voltammetry measurement at room temperature (about 23 ° C.) under the condition of a sweep rate of 5 mV / sec. The width of the potential window (potential width) obtained from the difference between the oxidation potential and the reduction potential of each electrolyte was defined as electrochemical stability. The results are shown in Table 1.

  The electrolyte containing the lithium polymer salt obtained in Examples 1 to 4 and the lithium polymer battery including this as an electrolyte layer have a high cation transport number. In addition, the lithium polymer salt obtained in Examples 1 to 4 was easily soluble in the fluoropolymer even at room temperature.

It is a schematic cross section which shows the basic composition of suitable one Embodiment of the lithium polymer battery of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Lithium polymer battery, 2 ... Anode, 3 ... Cathode, 4 ... Electrolyte layer, 5 ... Anode collector, 6 ... Cathode collector.

Claims (3)

Hexamethyldisilazane lithium represented by the following formula (a), a lithium polymer salt obtained by reacting only a compound represented by the following formula (b) , an aprotic solvent, and the lithium polymer salt only it contains and another polymeric material and,
An electrolyte in which the polymer material is a fluoropolymer having a repeating unit represented by the following general formula (2) .
[In the formula ( b ), A ¹ and A ² each independently represent a carbonyl group or a sulfonyl group, and R ¹ and R ² are an alkylene group, an arylene group, an alkenylene group or an alkylene ether substituted with a fluoro group. Indicates a group . ]
An electrochemical device comprising the electrolyte according to claim 1 as an electrolyte layer. The electrochemical device according to claim 2 , wherein the electrochemical device is a lithium polymer battery.